Method of preparing a blank for a conically shaped diaphragm



May 13, 1952 J. B. BRENNAN 2,596,354

METHOD OF PREPARING A BLANK FOR A CONICALLY SHAPED DIAPHRAGM Filed Sept. 9. 1946 IN V EN TOR.

A TTORNEY Patented May 13, 1952 UNITED STATES iATENT OFFICE METHOD OF PREPARING A BLANK FOR A CONICALLY SHAPED DIAPHRAGM Joseph B. Brennan, Bratenahl, Ohio Application September 9, 1946, Serial No. 695,806

3 Claims. 1

This invention relates to articles integrally formed of fibrous material. This application constitutes a continuation-in-part of my copending application Serial No. 422,388, filed December 10, 1941 and which has issued as United States Patent No. 2,408,038 on September 24, 1946, which application was a continuation-in-part of my application Serial No. 121,604 and was filed January 21, 1937, now abandoned. The invention is described herein with particular reference to the manufacture of acoustic diaphragms and to the manufacture of blanks from which acoustic diaphragms can be readily produced. It is to be understood that the invention is not limited to the particular articles disclosed herein.

According to present practice acoustic diaphragms are at present manufactured of fibrous materials according to either one of the two following methods:

1: A cutout blank is made of a piece of paper which is spliced into a somewhat conical shape using cement to effect the splice and this blank is subsequently shaped in a piece and otherwise treated to make the finished acoustic diaphragm.

2: A seamless hollow blank is accreted on a screen to the approximate shape of the finished article desired and is subsequently trimmed and treated to make the finished acoustic diaphragm, there being no splice in the diaphragm made in this way.

The objection to the first above-noted method is that the splice in the conical portion of the finished diaphragm unbalances the diaphragm as well as serving an awkward and expensive method of making the diaphragm. The second method is acceptable but the processes involved in making it are extensive and costly and the concentration and distribution of binders has not been easy to regulate.

Heretofore the application of binders has been done by dipping and could not be finely distributed so that the range of application and the number of fibers in contact with the binder materials in a certain area was not possible to regulate accurately. Hence stretch could not be had in blanks heretofore.

The present invention overcomes both the objections above-mentioned and devises a structure composed of intermingled or heterogeneously arranged textile fibers bonded to each other by the intermingling of thermoplastic particles which are distributed preferably by spraying or squirting throughout the fibrous structure. In certain areas the bonding thermoplastic particles are so distributed as to produce flexible sections and 2 in certain areas are so distributed as to give stiffmess.

The object of this invention is to provide a more economical and efficient method of producing hollow articles such as blanks for acoustic diaphragms which results in a more uniform product and a lower cost product. Another object of my invention is to provide a method of making hollow articles wherein the thickness of various sections may be varied although the articles are integral. Another object of my invention is to make a blank as for an acoustic diaphragm which can be subjected to heat and pressure and cured to its final shape. Another object of my invention is to make a blank for a hollow article such as an acoustic diaphragm which can be distorted at least 20% to 30% under heat and pressure. Another object of my invention is to provide articles formed integrally of deposited fibrous material having areas of widely varying rigidity. Another object of my invention is to provide a hollow blank formed integrally of fibrous material having a relatively rigid conical section and a relatively flexible flange to act as a suspension therefor. Another object of my invention is to eliminate or substantially cut down greatly the amount of liquid mediums now used to suspend fibers for deposition in the making of hollow fibrous articles such as acoustic diaphragms. Another object of my invention is to make a blank for an acoustic diaphragm which has improved wet strength. Another object of my invention is to make an acoustic diaphragm which is moisture resistant.

My invention involves the production of hollow articles from fibrous materials such as fibers of cotton, rayon, kapok, wool and wood and other textile fibers by the simultaneous but separate spraying of such fibers or a mixture thereof in the substantially dry state with a binder such as cellulose acetate or resins or plastic materials or latex upon a form and either compacting the deposited binder in the fibrous material and the deposited fibrous material upon said form while subjecting it to heat and pressure or removing it from the form upon which the layers were deposited and subjecting it to heat and pressure to compact and shape in a mold. Preferably the operation of depositing the blank is carried out by means of a number of spray devices or ducts placed closely together and directed to cover the form. At least one spray device is employed to discharge fibrous material in dry form and another spray device is employed to discharge the binding material. The separate spraying of the fibrous material and the binder enables the spraying operation to be carried out in the proportions desired and to regulate easily the deposition of fibers and the deposition and distribution of the binder. A solvent may be used with the binder to facilitate spraying and distribution or the binder may be rendered liquid by heat and ejected from the spraying device through fine orifices under hydraulic pressure or the binder may be applied in particles.

Gas pressure may be used also as a spray medium and heated steam may be used as a heating means and liquidifying or softening means for the binder as well as to assist in the atomization of the binder. Attenuated filaments of the binder may be produced by these spray devices or a fog may be produced of very fine particles of the binder under hydraulic pressure and heat. In other words, the form in which the binder is sprayed can be regulated so that it is necessary to use only a minimum of binder material to produce a strong and stretchy fibrous layer suitable for use in making a hollow acoustic diaphragm. The spray device used to apply the fibrous material may be so situated and directed that the fibrous layer applied by one device will have its fibers crossed at an angle by the fibrous layer deposited by another device so that a certain amount of cross-lapping and interlacing of the fibers is affected. Lamination is also possible. The binding material may be applied in such a way that only a very few of the fibers deposited come in contact therewith or it may be applied in such a way and in such proportions that all or nearly all the dry fibers come in contact therewith and are bound thereby. Immediately after completion of the deposition of the layers wanted on a base or form, the material so deposited may be removed and subjected to heat and pressure as for instance to make an acoustic diaphragm. The material so produced can be varied extensively so that it has considerable stretch and flow and can be molded to make the shapedesired and of the thicknesses desired. Water resistance can be also developed to the degree desired. Porosity can also be regulated to the degree desired. Due to the amount of stretch in the blanks made according to my process seamless hollow acoustic diaphragms can bemolded from flat material in certain cases and from blanks which only roughly approximate the finished article in other cases. When the blank is initially deposited it can be handled immediately thereafter and subjected to heat and pressure as in a mold. The fibrous material may consist of wood, cotton, rayon, wool or synthetic fibers or a mixture of paper or textile fibers. Binders, preferably thermoplastic, may consist of lacquers or resins, natural or synthetic, various plastic materials or rubber-like materials. A number of binders as well as a number of fibers each having different characteristics may be used to make the same blank or hollow articles such as an acoustic diaphragm. Different materials or combination of materials may be used for different areas of the same integral article to produce desired characteristics. Thus the hollow body portion of an acoustic diaphragm may be madeof a mixture of cellulose acetate binder and cotton fibers, the cellulose acetate being partially applied as a liquid and partially appied in small particles or filaments. Thermoplastic materials such as cellulose acetate may be applied or intermingled with the fibers having a certain content of a gas-producing agent such as ammonium carbonate mixed therewith so that when subsequently subjected to heat, the ammonium carbonate will produce a cellular structure due to the evolution of gas and its retention by the thermoplastic walls within a mold. Thus a very lightbodied structure can be effected possessing relative rigidity, which is very desirable in certain sections of an acoustic diaphragm. In any case after the mixtures of fibers and binders has been deposited the material so deposited may be further pressed and molded under heat and greatly distorted.

A conical diaphragm made according to my invention may be tapered in thickness radially in its conical body section so that it is thicker near the apex and thinner near the base of the conical section. The deposition of the fibrous materials and binders may be carried out on either male or female forms. These forms may be perforate or porous or solid and suction may be applied to these forms during the deposition of these ma terials and the forms may be moved to facilitate the deposition and distribution of these materials. The connection between the voice coil support and conical section of an acoustic diaphragm may be reinforced at will and the length of the voice coil support and shape thereof can be regulated at will according to my invention. Diaphragms made according to my invention can be molded to finished shape without trimming which is at present resorted to as being necessary in the manuiacture of integral acoustic diaphragms. They can be cured and finished on the form on which the original deposition is made in for example less than 5 seconds. A voice coil such as is used in connection with acoustic diaphragms can be incorporated in its proper location in a tubular neckpiece at the apex of the conical portion of the diaphragm at the time of deposition of the fibrous material and binder or an annular recess may be incorporated in the diaphragm at the time of deposition of the fibrous material and binder and the voice coil may be wound in this annular recess subsequently. The terminals of the voice coil may also be imbedded in the fibrous and thermoplastic layer of the conical body portion at the time of deposition of the fibers and thermostatic materials. The corrugations which are usually placed in the edge of hollow acoustic diaphragms can be molded as deep as desired due to the fact that the material deposited has at least 20 to 30% stretch when heated. The mold used in final shaping of acoustic diaphragms may be heated with steam or electrically or otherwise. In general, I have found that diaphragms made according to my process comprise by weight about to fibrous materials and 5% .to 10% binder material. However, in certain areas and for certain applications these amounts maybe varied widelydepending on the use intended. According to present practice a great deal of vacuum is required in making acoustic diaphragms by accreting fibers or pulp on a foraminous base. Whereas with my method vacuum can be dispensed with entirely although a little may be helpful; and no water is necessary, whereas great quantities are necessary in making either blanks or acoustic diaphragms according to present practice. Coaxial flanges at the periphery of the diaphragm can be readily and easily produced integrally with the rest of the acoustic diaphragm by my method. This can be accomplished only with great difiiculty by present methods.

Briefly, what I do is to incorporate nonbinder fibers dry or substantially dry with binder particles of thermoplastic materials to make hollow molded fibrous articles having relatively stiff and pliable areas and areas of differing thicknesses as Well as ,areas of different density. Also by my process fiat blanks or sheets can be made and subsequently distorted in a mold under heat and pressure to produce a finished shape. Or intermediate shaped blanks can be made by my invention and readily distorted under heat or pressure to the desired shape. In some cases Where extreme distortion is desired moistening of the blank prior to pressing is helpful.

Forming by deposition and rolling a fiat sheet with heat after deposition of binder thermoplastie and fibers and subsequently adding lacquers and/or thermoplastic solutions prior to molding is also contemplated according to my invention. By this method fiat sheet material can be made in lengths and stored until used. Wetting this sheet prior to or during pressing assists in the distortion to form the finished shape of the acoustic diaphragm. This sheet may be wetted with thin thermoplastic liquids to assist in molding and waterproofing prior to pressing.

Preheating of the fibers and thermoplastic materials to facilitate production can be resorted to when desired according to my invention.

It is according to my invention to be understood that fibers of any length can be used to make the blank and a mixture of fibers as to length, size, and density may be used.

Also it is to be understood according to my invention that fibers may be laid in single layers on end or with ends sticking up and rolled down in alternate direction with heated rolls so that one layer of fibers is at an angle to the adjacent layer which is rolled in another direction after deposition and bonded in this angular relationship by the thermoplastic binder.

The heat used in the mold should be sufilcient to soften the thermoplastic binder.

Thermosetting plastics may be used if only partly reacted prior to application and in this case the heat of the mold should be sufficient to cure.

The method and article of the invention are illustrated in the accompanying drawing in which;

Figure 1 is a partial sectional view illustrating formation of the blank; and

Figure 2 is a similar view illustrating the final forming operation.

As shown in Figure 1, the blank may be formed on a conical foraminous form such as a fine screen H1. The screen is supported at its periphery on a ring H which is rotatably mounted on a suction box [2. A conduit l3 connects the interior of the ring II and the lower surface of the screen H) to a vacuum pump or other source of vacuum. Except for the particular shape of the screen this construction is substantially similar to that disclosed in my Patent No. 2,408,038.

The dry fibers are sprayed onto the screen through a plurality of nozzles M which are spaced around and above the screen. As shown, more nozzle may be located near the apex of the screen than adjacent its periphery to form a conical blank l5 which tapers in thickness from its apex to its periphery. The binder is sprayed simultaneously with the fibers through nozzles it which are located adjacent to the nozzles l4 and are spaced to produce the desired distribution of binder. Thus, the nozzles l6 may be arranged to deposit more binder in proportion to the mass of fibers adjacent to the apex of the of the desired thickness, the blank is removed and placed in a mold as shown in Figure 2. This mold comprises a hollow base H through which heating fluid may be circulated through pipes l8. The top of the base is formed by a generally conical plate I9 whose upper surface is shaped to conform to the desired diaphragm shape. As shown, the plate [9 provides a central substantially cylindrical portion 2| to form the neck of the diaphragm, a corrugated edge portion 22, and an annular intermediate shoulder 23.

A hollow ram 24 completes the mold and may be heated by circulation of heating fluid through pipes 25. The ram has a lower conical closure plate 26 generally complementary to the plate [9 to leave a space between them corresponding to the desired diaphragm shape when they are brought together. As shown, the conical tapers of the two plates are slightly different to form a diaphragm as indicated at 21 which tapers in thickness from its apex to its rim.

As the mold parts are brought together on the blank it will be shaped and compressed to the desired final shape. During this operation the binder particles are made soft and adhesive due to the heat and pressure to bind the fibers together at spaced points. After the molding operation, the diaphragm may be varnished or otherwise sealed and is then ready for use.

Having described my invention what I claim 1s:

1. The method of preparing a blank for a conically shaped diaphragm comprising the steps of collecting separated fibers on a foraminous form, connected to means for evacuation, as a layer 7 in which the fibers are haphazardly arranged in interrnatted relation, and dispersing finely divided resinous binder particles with the fibers prior to their deposition whereby the binder particles collect at spaced apart points on the surfaces of the fibers, the arrangement of fibers and binder particles being such as to enable the layer subsequently to be shaped to conical form with the binder particles securing the fibers together at spaced apart points.

2. The method of preparing a blank for a conically shaped acoustical diaphragm comprising the steps of spraying dry fibers from separate sources onto a conical form in greater quantities adjacent to the apex of the form than at points spaced from the apex to provide a layer tapered radially in thickness from the apex of greater wall thickness to the base of least wall thickness, and spraying dry finely divided resinous binder particles on the fibers prior to deposition to collect in spaced apart relation on the surfaces of the fibers where they are able to secure the fibers together.

3. The method of preparing a blank for a conically shaped acoustical diaphragm comprising the steps of spraying dry fibers from separate sources onto a conical form in greater quantities adjacent to the apex of the form than at points ass-mam having a wall thickness tapered ;f:r,cm the apex of greatest wall thickness to the base of least wall thickness, :and sprayingw dry finely divided thermoplastic resinous binder in a predetermined patternicn the fibers ,tdprovide esincus binder at spaced-apart points on the surfaces of the fibers in varying concentrations Where they are able tosecure the fibers-together to form a prodnot with varying characteristics.

JOSEPH B. BRENNAN.

B REFERENCES CITED The following references are of record in the We of this patent:

.8 UNITED STATES ,BA'IENTS Number Name Date Werking 'Jan. 4, 1927 Huff et al. Dec. 3, 1935 Carter Apr. 1, 1941 Shoeld Dec. 8, 1942 Nielsen Sept. 7, 1943 Maxwell Dec. '14, 1943 Francis, Jr. Sept. 5, 1944 Koon Mar. 27, 1945 Francis Jan. 25, 1949 Castellan July 19, 1949 

